Method and apparatus for determining chrominance space

Abstract

A method for determining which one of regions in a chrominance space an input point belongs to. The regions are defined by boundary lines. The method includes generating in the chrominance space a first line, extending through the input point and the origin of the chrominance space, and a second line, connecting a point on the Cb axis of the chrominance space and a point on the Cr axis of the chrominance space. The method further includes comparing coordinates of a first intersection point, at which the first line and the second line intersect, and coordinates of second intersection points, at which the second line and the boundary lines intersect, to determine the region to which the input point belongs.

1. A chrominance space region determination method performed by a chrominance space region determination apparatus for determining which one of regions in a chrominance space an input point belongs to, the chrominance space having, a Cb axis, a Cr axis, and an origin which is an intersection of the Cb axis and Cr axis, and the regions being defined by boundary lines each of which extend from the origin on a Cr-Cb area including the Cb axis and Cr axis, the method comprising:
 computing, with a coordinate calculation unit of the chrominance space region determination apparatus, a coordinate of a first intersection point in the chrominance space at which a first line extending through the input point and the origin intersects with a second line connecting a point on the Cb axis and a point on the Cr axis; 
 comparing, with a determination device of the chrominance space region determination apparatus, a coordinate of a first intersection point at which the first line and the second line intersect, and coordinates of second intersection points at which the second line and the boundary lines intersect, to determine the region to which the input point belongs. 
 
     
     
       2. The chrominance space region determination method according to  claim 1 , wherein the chrominance space is a Cb-Cr space, and the second line is represented by the expression of Cb+Cr=2k (k=1, 2, 3, . . . ). 
     
     
       3. The chrominance space region determination method according to  claim 1 , wherein the chrominance space includes a first quadrant, a second quadrant, a third quadrant, and a fourth quadrant, and said comparing includes converting, with a quadrant converter of the chrominance space region determination apparatus, the coordinates of the first intersection point and the coordinates of the second intersection points to coordinates in the first quadrant when the input point is located in one of the second to fourth quadrants and comparing, with the determination device, the converted coordinates of the first intersection point with the converted coordinates of the second intersection points. 
     
     
       4. The chrominance space region determination method according to  claim 3 , wherein said comparing includes:
 determining, with the determination device, which one of the first to fourth quadrants the input point is located in based on coordinates of the input point; 
 when the input point is located in a quadrant other than the first quadrant, converting, with the quadrant converter, the coordinates of the input point based on the determination result to coordinates corresponding to the first quadrant; 
 selecting the coordinates of the second intersection point corresponding to the quadrant the input point is located in based on the determination result; and 
 comparing, with the determination device, the selected coordinates with the coordinates of the input point. 
 
     
     
       5. The chrominance space region determination method according to  claim 1 , wherein said comparing includes comparing a Cb coordinate of the first intersection point and a Cb coordinate of the second intersection point without comparing a Cr coordinate of the first intersection point and a Cr coordinate of the second intersection point. 
     
     
       6. A chrominance space region determination apparatus configured to determine which one of regions in a chrominance space an input point belongs to, the chrominance space having, a Cb axis, a Cr axis, and an origin which is an intersection of the Cb axis and Cr axis, and the regions being defined by boundary lines each of which extend from the origin on a Cr-Cb area including the Cb axis and Cr axis, the apparatus comprising:
 a coordinate calculation unit configured to compute a coordinate of a first intersection point in the chrominance space at which a first line extending through the input point and the origin intersects with a second line connecting a point on the Cb axis and a point on the Cr axis; and 
 a determination device configured to compare the coordinate of the first intersection point with coordinates of second intersection points at which the second line and the boundary lines intersect to determine the region to which the input point belongs. 
 
     
     
       7. The chrominance space region determination apparatus according to  claim 6 , wherein the coordinate calculation unit includes:
 a quadrant determiner for determining the quadrant to which the input point belongs to based on coordinates of the input point; and 
 a quadrant converter for converting, when the input point is located in a quadrant other than a first quadrant, the coordinates of the first intersection point and the coordinates of the second intersection points to coordinates in the first quadrant.